1. Field of the Invention
The present invention relates to an organic solar cell, and in particular relates to an organic solar cell which has high photoelectric conversion efficiency.
2. Description of the Related Art
Currently the energy used to generate electricity around the world is based on non-renewable energy, such as petroleum, natural gas, coal or nuclear energy, which causes serious pollution problems. Therefore, non-polluting, renewable energy sources such as hydropower, wind power, geothermal power, ocean energy, biomass energy and solar energy have become more important. Among them, solar energy is most often used to replace the existing non-renewable energy sources due to its wide distribution and easy obtainment.
Light energy is directly absorbed and converted to electric energy by using a solar cell which is made up of solid semiconductor components. The basic structure of the solar cell is the semiconductor pn junction formed by the contact between p and n-type silicon. When sunlight hits the solar cell, the semiconductors absorb photons to excite electron-hole pairs (also refers to excitations). As a result of the internal electric field effect, the holes and electrons respectively transport toward opposite cathode and anode and aggregated. The anode and cathode are electrically connected to output loading circuits and electric power is generated.
At present, the solar cell has developed three generations: the types of first generation are silicon-based solar cells which are based on single crystal silicon, polysilicon, or amorphous silicon; the second generation are the hybrid solar cell which are based on GaAs, CdSe, CuLnGaSe2 and some inorganic semiconductor compounds; the third generation are the organic solar cells which are based on dye-sensitized materials, conducting polymers and conjugated polymers.
The advantages of the organic solar cell include; a simple process, low cost, light weight, flexibleness, large area production and potential for high conversion efficiency (theoretically up to 20% in future). However, the main shortcoming is its low practical conversion efficiency. Thus, there are many approaches to improve the practical photoelectric conversion efficiency of the organic solar cell. Among these approaches are; changing the preparation of materials, carrying out some particular processes (i.e. annealing or film treatments), or adding some specific structures into the solar cell devices.
In Solar Energy Materials and Solar cells, 37, 1995, 337-348, O. Stenzel and A. stendal et al. showed adding a metal film into the organic solar cell, such as coating a thin metal film on the surface of the anode (tin indium oxide), which effectively increased the generation of photocurrent and the photoelectric conversion efficiency of the organic solar cell. The metal film surface excited the production of surface plasmons which may enhance the localized electromagnetic field which increases the photon absorption efficiency of the active layer.
In Applied Physics Letters, 92, 2008, 244304, Anthony J. Morfa and Kathy L. Rowlenam et al showed a method of coating metal nanoparticles on the surface of the anode (tin indium oxide), which further increased the photoelectric conversion efficiency of the organic solar cell.
Therefore, at present, there is a need for an organic soar cell which can further control the effective surface plasmon effects to achieve a higher photoelectric conversion.